The present invention relates to a semiconductor photodetector using SITs (Static Induction Transistors), and to a method for driving the same. More particularly, the invention relates to an improvement in such a photodetector for providing nondestructive data readout.
A basic semiconductor photodetector using SITs to form a solid-state image pickup device is disclosed in Japanese Laid-Open Patent Application No. 15229/1980. Improvements of that device have been disclosed, for instance, in Japanese Patent Application No. 204656/1981.
In such an SIT semiconductor photodetector, carriers produced by incident light are not directly outputted as data. More specifically, data is read out in such a photodetector by varying the source-drain current of the SITs according to the amount of carriers accumulated during a reading operation. Thus, a semiconductor photodetector of this type has a feature that the data can be read out nondestructively. This nondestructive readout is effective in the optical detection of still pictures using a line sensor or an image sensor.
In a conventional photodetector composed of SITs, especially a photodetector in which a plurality of SITs are arranged one or two dimensionally, carriers produced by incident light are accumulated in the gate region (in the control gate region in the case of a gate division type photodetector), and current is caused to flow between the source and the drain by applying a voltage to the gate region. The voltage applied to the gate region causes carriers accumulated therein to be discharged into the channel region. If a voltage is applied to the gate for a sufficiently long time or a sufficient number of times, the carriers will be depleted. It is considerably difficult to maintain conditions such as a magnitude and a pulse width for the data reading voltage applied to the gate region to retain a sufficient charge in the gate region, which makes it difficult to read out the data in a nondestructive mode.
Accordingly, an object of the invention is to provide a semiconductor photodetector in which the above-described difficulties accompanying a conventional semiconductor photodetector have been eliminated and data can be satisfactorily read out in a nondestructive mode. The invention further relates to a method for driving such a semiconductor photodetector.